It is known to provide cameras which are designed so that the Scheimpflug condition is substantially met to enable providing an image to a film which is in focus over a large film area even though the source of the image is spatially distributed over varying distances from the camera lens. It is also known that when a beam of electromagnetic radiation is directed to a sample at an oblique angle of incidence, if, for instance it is essentially circular at the source thereof, then it appears as an ellipse at a sample surface. The shape of the spot on the sample can be modified by providing an elliptically shaped aperture at the source, or alternatively, by rotating an aperture with a circular hole therein to appear to the beam as an ellipse or some combination thereof. Properly orienting such an aperture will preshape the source beam so that when it impinges on the sample an essentially circular spot is achieved.
A Patent to Horie, U.S. Pat. No. 7,095,498 describes the presence of a pinhole mirror in a spectroscopic ellipsometer system. The pinhole mirror is rotated so that a beam of electromagnetic radiation is oriented along a locus which is oblique angle, rather than along a normal thereto.
A Patent to Masao, U.S. Pat. No. 5,963,326 describes an imaging ellipsometer which uses a large cross-section measuring beam rather than a small beam spot as is the focus in the present invention.
A Patent to Finarov, U.S. Pat. No. 5,517,312 mentions the Scheimpflug condition in the context of a scanning ellipsometer wherein a beam is scanned over a sample and a pattern recognition camera which is designed to utilize the Scheimpflug condition is applied.
Also disclosed is a Patent to Wielsch, U.S. Pat. No. 6,897,955 and related Application PCT WO01/86257 and Patent DE 10023411 which describe a rectangular aperture opening to make a square measurement spot. The opening is adjustable in size and geometry but there is not mention of tilting the aperture.
The prior art does not, to the Inventor's knowledge, describe applying the Scheimpflug condition to design of reflectometer, ellipsometer, polarimeter or the like systems, especially when combined with tailoring the shape of an aperture to provide a sharply focused circular spot at a sample when it is oriented as require to meet the Scheimpflug condition.
Need exists for improved a system and method of providing electromagnetic radiation to a sample and/or detector wherein focus is achieved over substantially the entire area of a spot of electromagnetic radiation impinging thereupon.